1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of driving the same.
2. Discussion of Related Art
A liquid crystal display device is a flat panel display device having liquid crystal cells arranged in a matrix between an upper substrate and a lower substrate.
The liquid crystal display device forms an electric field by applying a source voltage and a common voltage to a pixel electrode and a common electrode, respectively, of liquid crystal cells selected by a scan pulse, and then controls transmittance of light supplied from a backlight assembly according to arrangement angles of corresponding liquid crystals to display an image.
Here, the source voltage is a data signal of the liquid crystal display device, and brightness of light emitted by the liquid crystal cells varies depending on the magnitude of the source voltage.
The source voltage is supplied from a source driver (data driver) and is output from a source amplifier (SAP) provided in an output terminal of the source driver to be supplied to a data line.
However, the rising slope of the source voltage output from the source amplifier is controlled by a source amplifying register (SAP register). The source amplifying register is a register which controls the output of the source amplifier. More specifically, the source amplifying register controls the output of the source amplifier depending on a preset source amplifying set value (SAP value).
In particular, in a conventional liquid crystal display device, driven at room temperature, the source amplifying register controls the output of the source amplifier corresponding to a preset source amplifying set value such that a source on-time for the liquid crystal cells can emit as much light having brightness corresponding to the source voltage as can be secured. For example, the source amplifier may register level 3 or level 4 source amplifying set values from among source amplifying set values between, for example, level 1 and level 5, and control the output of the source amplifier corresponding thereto.
Here, the source on-time means time taken to raise the source voltage to the voltage of the corresponding data and then to maintain the voltage.
If the source-on time described above is long, the liquid crystal cells may sufficiently represent the brightness corresponding to their relevant data, while power consumption increases as the source on-time becomes longer. Therefore, the source amplifying register designates a rising slope of the source voltage depending on the source amplifying set value, with a level optimized based on brightness representation and power consumption of the liquid crystal display device when driven at room temperature. Here, the source amplifying set value may be designated as a value of rising time or rising slope, and be referred to as a value designated as the rising slope of the source voltage.
However, although the source amplifying set value described above is preset, the rising slope of the source voltage output from the source driver may be varied depending on changes in ambient temperature.
More specifically, since the source amplifying set value is set based on room temperature, it cannot be controlled based on changes to ambient temperature. Therefore, when the ambient temperature of the liquid crystal display device becomes low, the mobility of a thin film transistor (hereinafter referred to as a TFT) constituting the source amplifier deteriorates to control the source amplifier depending on the fixed source amplifying set value, without reflecting the generated deterioration of the driving capability of the source amplifier. Therefore, since the rising slope of the source voltage is reduced corresponding to the reduction in power consumption generated as the ambient temperature falls, data lines and liquid crystal cells cannot be readily charged with the source voltage.
In other words, when the ambient temperature becomes low, the rising slope of the source voltage is reduced, causing the source on-time to be short, thereby causing charge errors of the source voltage from the panel, as shown in FIG. 1. Vertical line defects are thereby generated from a display unit showing an image. In FIG. 1, Vg represents scan pulse, Vc represents common voltage, and Vs represents source voltage.
In contrast, when the ambient temperature becomes high, the mobility of the TFT constituting the source amplifier increases to cause an increase in the rising slope of the source voltage, thereby causing a problem where current consumption increases.